This proposal requests support for a Keystone Symposia meeting entitled Immunologic Memory, Persisting Microbes and Chronic Disease, organized by E. John Wherry, Bali Pulendran and Yasmine Belkaid, which will be held in Banff, Alberta, Canada from February 6-11, 2011. This meeting is focused on the overall theme of understanding how immunological memory develops and how this development is influenced by the microbial world around and within us. Immunological memory can provide potent protection from infectious disease. Many infections are cleared rapidly by the immune system leaving the host with protective B and T cell memory. However, other host-pathogen interactions are long-term and can develop into chronic diseases. Immunological memory develops differently during these protracted infections. Prolonged host-pathogen interactions, chronic infections and co-infection with multiple pathogens can impact the host's immune system in ways that remain incompletely understood. Moreover, the universe of microorganisms with which our immune system interacts includes not only pathogens, but also normal bacterial and viral commensal flora. The impact of these microorganisms on immunological memory is only just starting to be evaluated. The goals of this meeting are to discuss: 1) cutting-edge research on the mechanisms of optimal immunological memory;2) the impact of prolonged host-microbe interactions on immunological memory;and 3) how the application of cutting-edge approaches to studying these issues can help generate better vaccines and immunotherapies. Project Narrative: Immunological memory can provide potent protection from infectious disease. Understanding how to induce optimal immune responses through vaccination and other therapeutic interventions holds tremendous potential for treating and/or preventing viral, bacterial and parasitic infections, cancer and other diseases. The Keystone Symposia meeting on Immunologic Memory, Persisting Microbes and Chronic Disease is focused on the overall theme of understanding how immunological memory develops and how this development is influenced by the microbial world around and within us.